Nitronium perchlorate propellant composition

ABSTRACT

1. A PROCESS FOR PREPARING A PROPELLANT CONTAINING NITRONIUM PERCHLORATE AND A POLYMERIC BINDER COMPRISING ADDING A PERDETERMINED QUANTITY OF GROUP IA METAL TO SAID PLYMERIC BINDER WHEREBY SUBSTANTIALLY ALL THE WATER IN SAID BINDER REACTS WITH THE GROUP IA METAL TO FORM A HYDROXIDE AND SUBSEQUENTLY ADDING TO SAID POLYMERIC BINDER A PREDETERMINED QUANTITY OF NITRONIUM PERCHLORATE.

United States Patent O1 ice 3,575,744 Patented Apr. 20, 1971 Int. Cl. C06d /00 US. Cl. 149-19 2 Claims This invention relates to an improved propellant composition and the method of incorporating uncoated nitronium perchlorate into a polymeric binder to produce a unique propellant composition.

In the past, the use of nitronium perchlorate with elastic organic binders such as polybutadiene has met with considerable difiiculty. Water, invariably found in small quantities in the binder, combines with nitronium perchlorate to produce reaction products that degrade the physical properties of the binder. To avoid this reaction of nitronium perchlorate with the water content of the binder, it has previously been the practice to produce nitronium perchlorate in the form of spheres or other particulate shape which are subsequently coated with a water-proofing material such as polymeric plastic.

The present invention, however, eliminates the need for coating particles of nitronium perchlorate. It has been found that by using high energy metal such as lithium in conjunction with the nitronium perchlorate and binder the 'water in the system will preferentially react with the lithium leaving substantially no residual water to react with the nitronium perchlorate. In addition, it has been found that the high energy metals are instrumental in ouring the binder and, moreover, have the inherent capacity to enhance the specific impuse of the propellant.

It is an object of the present invention, therefore, to provide a unique process for making a solid propellant which can employ uncoated nitronium perchlorate. An additional object of the present invention is to provide a process for mixing propellants containing nitronium perchlorate and a polymeric binder. A further object is to provide a propellant additive which will improve the curing characteristics of the binder and enhance the thrust characteristics of the propellant. A still further object is to provide a propellant composition which employs uncoated nitronium perchlorate in combination with organic binders.

Basically, the invention contemplates the preparation of solid propellant charges comprised of nitronium perchlorate, a hygroscopic high-density oxidizer, and commercial organic polymers containing small quantities of 'Water. To achieve this end, high energy metals from Groups I-A of the Periodic Table, such as lithium, are employed to scavenger the water which would otherwise combine with the nitronium perchlorate creating reaction products incompatible with the binder.

Binders suitable for propellant charges are usually organic materials which possess elastic properties whereby desirable physical characteristics are imported to the propellant. Typical binders finding wide application are olefinic elastomers such as polybutadiene; the elastic properties of organic polymer are primarily due to an unsaturated carbon to carbon bond as shown in the graphic formula for polybutadieue:

(1) H H H H Patna...

The double carbon to carbon bond, responsible for the elasticity of the cured material, is, unfortunately, readily degraded to a single bond by the presence of certain reactive impurities in the binder. Impurities posessing a relatively high ionization constant will attach to one of the double-bonded carbon atoms, thereby diverting one of the two bonds. For example, mixtures of nitric acid and perchloric acid degrade polybutadiene in a variety of manners such as:

I H OH l loz H These reaction products, nitric acid and perchloric acid, then attack the polymeric binder to destroy the double bond as exemplified in Equation 2.

The prior art practice of the encapsulating pelletized or granular nitronium perchlorate in a water-proof plastic polymer tends to minimize the above reaction with water. However, the present invention achieves improved results by employing a high energy metal as a water scavenger to deprive the nitronium perchlorate of water with which to react to produce the undesirable degrading agent. For example, by adding lithium to the propellant mix, the water in the system is preferentially consumer as follows:

The resultant bi-product, LiOH, is a stable hydroxide which cannot be attacked by nitronium perchlorate to reverse the reaction. Consequently, by employing lithium or other high energy metals as a getter or scavenger in the propellant system, to the extent that all water from any source whatsoever is consumed thereby, a stable propellant results possessing virtually no tendency to degrade on standing.

The minimum quantity of lithium suitable for oxidation is, of course, directly dependently upon the wetness of the specific liquid polymer. If the polymer is first treated to remove as much Water as possible by conventional techniques, such as azeotroping, smaller quantities of lithium can be employed. However, this additional step is not necessary with most commercial polymers since the quantity of water present is so slight that an addition of about one percent by weight of lithium will react with substantially all the water present. But, because of the density differential between lithium and the binder, a floatation problem exists often requiring, for the sake of convenience, the use of excessive lithium to assure an adequate distribution of lithium to tie up the water present. As to an upper limit in the use of lithium, no criticality exists since lithium is a highly desirable fuel in itself and may, therefore, be intentionally added in greatly excess quantities insofar as scavenging needs are concerned.

Because of the highly reactive nature of lithium with both oxygen and nitrogen in air, normally, in preparing a propellant, it is preferred to mix the lithium with the binder under a protective atmosphere such as ar-gon or helium having a dew point of -40 C. or lower. After thoroughly mixing the lithium and binder, nitronium perchlorate is added while still under the protective atmosphere. In this way the nitronium perchlorate particles,

as added to the lithium treated binder, will not be coated with the nitric acid, perchloric acid, and other salts caused by the reaction with atmospheric contaminants. However, even if these acids are found to some extent, the lithium will react with the acids to form harmless salts.

After adding the nitronium perchlorate to the lithium treated binder and mixing until substantially homogeneous, the liquid mixed is then poured into suitable molds or directly into motor casings. Curing is possible in some formulations by merely maintaining at room temperature for 24 hours or by holding at slightly elevated temperatures for correspondingly shorter times. After curing, the solid propellant is ready for use and may be stored for prolonged periods without fear of binder degradation.

In order that one skilled in the art may readily reproduce the results of the present invention, the following specific examples set forth in detail the method for preparing typical preferred formulations.

EXAMPLE 1 A solid propellant composition is formulated by mixing together approximately 30 percent by weight of polybutadiene having a molecular Weight of approximately 3,000 and a viscosity of about 300 poises (.it was found that curing was considerably facilitated by employing polybutadiene containing at least 0.4 milliequivalents of hydroxyl) 10 percent by weight of lithium particles on the order of 200 microns and 60 percent by weight of nitronium perchlorate in particulate spherical form of about 1,000 microns. The lithium particles are mixed in a protective atmosphere of argon having a dew point of 40 C. with the polybutadiene whereupon the lithium reacts with the water present in the binder. The nitronium perchlorate is then added and the ingredients are mixed until homogeneous. Still under the protective atmosphere of argon, the mix is poured into molds. Curing is effected by maintaining at room temperature for 24 hours since hydroxyl-containing butadiene is used and the lithium acts as a cure catalyst in such case.

EXAMPLE 2 A solid propellant composition is formulated by mixing together approximately 25 percent by weight of polybutadiene containing a miimnum of 0.4 milliequivalent of hydroxyl, 25 percent. by weight of lithium particles on the order of 200 microns, and percent by weight of nitronium perchlorate in particulates spherical form of 1,000 microns. The binder and lithium are first mixed in an argon atmosphere of a 40 C. dew point and then nitronium perchlorate is added to the mix. After thoroughly mixing, the formulation is poured into molds under the argon atmosphere. The propellant is then cured by holding at 50 C. for a period of 3 hours.

Other ingredients can, of course, be added to either dilute the effect of or add another effect which is characteristic of the material added. Consequently, various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter described by the appended claims, as only preferred embodiments thereof have been disclosed.

Having thus described the invention, what is claimed is:

1. A process for preparing a propellant containing nitronium perchlorate and a polymeric binder comprising adding a perdetermined quantity of Group Ia metal to said polymeric binder whereby substantially all the Water in said binder reacts with the Group Ia metal to form a hydroxide and subsequently adding to said polymeric binder a predetermined quantity of nitronium perchlorate.

2. A process for preparing a propellant composition comprising the steps of adding a predetermined quantity of lithium to an organic binder whereby substantially all the water entrained in said binder combines with the lithium to form lithium hydroxide and subsequently mixing nitronium perchlorate with said binder so treated.

References Cited UNITED STATES PATENTS 3,035,948 5/1962 Fox 14919 2,970,898 2/1961 Fox 14942X 3,006,743 10/1961 Fox et al. 149-36X BENJAMIN R. PADGETT, Primary Examiner U.S. Cl. X.R. 

1. A PROCESS FOR PREPARING A PROPELLANT CONTAINING NITRONIUM PERCHLORATE AND A POLYMERIC BINDER COMPRISING ADDING A PERDETERMINED QUANTITY OF GROUP IA METAL TO SAID PLYMERIC BINDER WHEREBY SUBSTANTIALLY ALL THE WATER IN SAID BINDER REACTS WITH THE GROUP IA METAL TO FORM A HYDROXIDE AND SUBSEQUENTLY ADDING TO SAID POLYMERIC BINDER A PREDETERMINED QUANTITY OF NITRONIUM PERCHLORATE. 